Source of phosphate for agriculture and the food industry

Abstract

A source of phosphate for agriculture and food industry comprises a phosphate salt in solid form of formula M_n(HPO4)y.zH2O in which M is Na, K, NH4, n=2, and y=1; or M is Ca, n=1, y=1; or M is Al or Fe, n=2, y=3; and in which z is 0, 1 or 2, wherein said phosphate salt has a phosphate content expressed as a P2O5 content of between 30 and 50% by weight of the phosphate salt, and it has a cadmium content lower than 0.40 ppm.

Description

TECHNICAL DOMAIN[0001]This invention relates to a phosphate salt having high purity, that is to say a low content of impurities, particularly radioactive impurities and / or impurities derived from heavy metals or transition metals of the Periodic Table of Elements. This invention also relates to a process for preparing said phosphate salt and its use in a formulation or a composition intended for agriculture or the food industry or for the preparation thereof. Preferably, said phosphate salt can be used for the preparation of single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), phosphoric acid, NPK fertilizer, monocalcium phosphate (MCP) or mono-dicalcium phosphate (MDCP).TECHNOLOGICAL BACKGROUND OF THE INVENTION[0002]Phosphate salts are regularly used in fertilizer compositions such as fertilizers or food compositions in order to facilitate phosphorus dispersion into the soil or into animal or human food respectively.[00...

AI Technical Summary

Benefits of technology

[0146]According to an alternative aspect of the invention, when said phosphate source used in step a) of this method is a secondary phosphate source such as fly ash derived from the incineration of bones, slurry or sludge purification as described in this application, the digestion using a hydrochloric acid solution (step a)) forms an aqueous solution comprising phosphate ions and chloride ions in solution. It can be isolated after step b) of the method. This solution is purified to remove the chloride ions to produce phosphoric acid or MCP. The chloride ions can be removed using the purification techniques known to those skilled in the art.

[0147]Procedure for Determining the Contents of Radioactive Elements by Gamma Ray Spectroscopy

[0148]The contents of Pb210, K40, R226 and R228 have been determined by gamma ray spectroscopy. The measurements have been performed using a detector comprising a high-purity germanium (HPGe) from the brand Canberra (HPGe XtRa with 50% relative efficiency or HPGe BEGe with 34% relative efficiency) and placed within a measuring device containing a lead shielding. The measurements are performed between 3 keV and 3 MeV for a BEGe detector or between 3 keV and >10 MeV for an XtRa detector. The detector is calibrated using samples placed in Marinelli™ containers with a capacity of 1 mL to 2.5 L. The contents of Ra226 have been determined by measuring “daughter” radionuclides of Ra226. The sample to be analysed is combined with activated carbon in water to absorb the Ra226 present in the sample. The solid residue is placed in a container (coaxial HDPE—250 mL) for 21 days. The measurement of Ra226 has been performed using a Lucas cell detector. The content of K40 is determined by the emission line at 1460.82 keV. The Ra226 content was determined based on the “daughter” radionuclides Bi214 and Pb214 whose emission lines are respectively located at 609.31 keV, 1120.28 keV and 1764.5 keV for Bi214 and at 241.99 keV, 295.22 keV and 351.93 keV for Pb214. The Ra228 content was determined by considering the emission lines of Ac228 at 338.32 keV, 911.19 keV and 968.96 keV. The Pb210 content was determined by considering the emission line at 46.5 keV.

[0149]Procedure for Determining the Contents of Radioactive Elements by Alpha-Particle Spectrometry

[0150]The contents of Po210, Th228, Th230, Th232, U234, U235, U238 were determined by alpha-particle spectrometry. The detector is a silicon detector also referred to ass a “PIPS detector” from Canberra. When the sample to be analysed is solid (e.g. DCP or CaS04), 1 g of the sample is previously digested using microwaves in the presence of a mixture comprising 5 ml of hydrofluoric acid, 5 mL of hydrochloric acid and 5 mL of nitric acid. When the sample to be analysed is liquid, it (10 mL) is treated with an aqueous solution of FeCl3 (1 mL of a solution prepared from 7.3 g / 100 mL). The precipitate is centrifuged and calcined. To determine the content of polonium Po210, the pre-treated sample mentioned above is mixed with 0.25 L of water and 20 mL of hydrochloric acid (6 M), ascorbic acid before being placed on a silver surface and stirred at a temperature between 80° C. and 90° C. for 6 hours. To determine the contents of uranium and thorium, the sample is purified on an ion-exchange resin (Biorad AG) in the presence of a tracer (Po208 and Po209) for removing polonium and subjected to a second separation between uranium and thorium on a column consisting of a UTEVA® resin (Eichrom) in the presence of a U232 and Th229 tracer.

[0151]Procedure for Determining the Contents of Transition Metals

Problems solved by technology

In the field of agriculture, fertilizers are nevertheless compounds that can cause serious damage to the environment, particularly cultivated land.

Given the intensive use of mineral fertilizers to increase supply of nutrients such as nitrogen or phosphorus, soils can be permanently contaminated if these nutrients contain excessive impurities.

The dispersion of these toxic elements in cultivated soils causes sustainable environmental pollution of said cultivated soils.

Excessively high magnesium content in the phosphate source i.e. greater than 1% by weight of magnesium in the phosphate source creates problems for treatment of the attack liquor during the leaching of the phosphate source with an acid.

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